When should I tell my work I'm pregnant?

Hi. I'm 13 weeks pregnant in a couple days. I haven't told anyone at work. I had a scan done at 10.5 weeks, and we saw the heartbeat and the baby moving. (although they couldn't get a heartbeat with the doppler, but said that was quite common since I was only 10 weeks) Anyway, I have another apointment at 14.5 weeks and the time IS GOING BY SOOOOOO SLOWLY by the way until then. I'm wondering if it's safe to tell my coworkers yet or should I wait to see if everything is okay. Geez, I am such a little worrier about this, is it just me? Anyone else felt the same and when did you tell everyone?